Non-viral sialidases. Sialidases or neuraminidases function to bind and hydrolyze terminal sialic acid residues from various glycoconjugates, they play vital roles in pathogenesis, bacterial nutrition and cellular interactions. They have a six-bladed, beta-propeller fold with the non-viral sialidases containing 2-5 Asp-box motifs (most commonly Ser/Thr-X-Asp-[X]-Gly-X-Thr- Trp/Phe). This CD includes eubacterial and eukaryotic sialidases.
Glycosyl hydrolase families 32 and 68, which form the clan GH-J. This glycosyl hydrolase family clan J (according to carbohydrate-active enzymes database (CAZY)) includes family 32 (GH32) and 68 (GH68). GH32 enzymes include invertase (EC 3.2.1.26) and other other fructofuranosidases such as inulinase (EC 3.2.1.7), exo-inulinase (EC 3.2.1.80), levanase (EC 3.2.1.65), and transfructosidases such sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99), fructan:fructan 1-fructosyltransferase (EC 2.4.1.100), sucrose:fructan 6-fructosyltransferase (EC 2.4.1.10), fructan:fructan 6G-fructosyltransferase (EC 2.4.1.243) and levan fructosyltransferases (EC 2.4.1.-). The GH68 family consists of frucosyltransferases (FTFs) that include levansucrase (EC 2.4.1.10, also known as beta-D-fructofuranosyl transferase), beta-fructofuranosidase (EC 3.2.1.26) and inulosucrase (EC 2.4.1.9). GH32 and GH68 family enzymes are retaining enzymes (i.e. they retain the configuration at anomeric carbon atom of the substrate) and catalyze hydrolysis in two steps involving a covalent glycosyl enzyme intermediate: an aspartate located close to the N-terminus acts as the catalytic nucleophile and a glutamate acts as the general acid/base; a conserved aspartate residue in the Arg-Asp-Pro (RDP) motif stabilizes the transition state. A common structural feature of all these enzymes is a 5-bladed beta-propeller domain, similar to GH43, that contains the catalytic acid and catalytic base. A long V-shaped groove, partially enclosed at one end, forms a single extended substrate-binding surface across the face of the propeller.
